Knucklehead97 Posted August 30, 2015 Posted August 30, 2015 I have two topics of questions today. 1, what all is required in swapping a 97+ C8.25 rear axle in? Really considering doing this soon because I want 3.55's. I've heard something about having to have the rear driveshaft shortened... What should I check for when looking at a junkyard axle in order to make sure it's worth the buy? And question number 2, what would 225's be like with 3.55 gears? I'm going to probably have to get ANOTHER set of tires soon... because the guy kind of screwed me on these used tires. I didn't check them enough before shaking his hand and I have just found small hairline dryrot all the way around the sidewall where it meets the tread and the rim, so crap bad deal once again... I'm thinking about getting a new set of 225's in the next couple months because I like how they look but I may regear to 3.55's soon as well. Just don't want to have to buy another set of new tires soon after a new set of 225's...
Knucklehead97 Posted August 30, 2015 Author Posted August 30, 2015 If 225's and 3.55's won't lower my gas mileage or anything then I would love to have that extra get up and go for a bit.
dunnc1991 Posted August 30, 2015 Posted August 30, 2015 8.25 swap is just relocating the leaf spring perches to the bottom of the axle. If I remember right, the 8.25 is 1" longer then a d35 so I wouldn't think the drive shaft would really be an issue lengthwise.
Incommando Posted August 30, 2015 Posted August 30, 2015 225/3.55 is a good combo for power and mileage. It is a very common 4.0/auto combo. The driveshafts are 1" apart IIRC. There is a chart for the different choices in the DIY section
Knucklehead97 Posted August 30, 2015 Author Posted August 30, 2015 I knew it was a usual auto combo, wasn't sure if it would fair as well for a stickshift. The rear axle swap sounds pretty plug and play other than the welding of the perches.
Knucklehead97 Posted August 30, 2015 Author Posted August 30, 2015 I really feel like an idiot for not checking these tires better. Waste of $65.
Eagle Posted August 30, 2015 Posted August 30, 2015 I knew it was a usual auto combo, wasn't sure if it would fair as well for a stickshift. The rear axle swap sounds pretty plug and play other than the welding of the perches. "225" is not a tire size. It's only one part of the size. You also need to know the profile ratio (the 70, 75, xx) part, and the rim size. Since you have an MJ, I guess we can live dangerously and assume that you have 15" rims. But those other two digits make a big difference. The largest factory tire size offered on XJ and MJs was a 225/75R15. That's what came on my 2000 XJ Sport. My wife's 2000 XJ Classic came with 16" rims. The factory tire size was 225/70R16. Note the change to a 70-series. The actual tire size, in diameter and in revolutions per mile, is the same as the 225/75R15. Yes, the 225/75-15s with 3.55 gears and a 5-speed makes a good combination. It's what the factory should have used, IMHO. The ridiculous gearing the factory used with the 5-speeds was chosen to beat some arbitrary fuel economy test. If you think about it, the factory combination has the engine turning over at 1821 RPMs at 65 MPH. That's well below the torque peak of the engine, and best economy is produced at the torque peak. With my '88 XJ 5-speed, I found the gas mileage didn't suffer if I "forgot" 5th gear entirely, and just drove on the highway in 4th. (Maximum legal speed around here is 65, and many highways through and around the cities it's 55. I wouldn't try the same experiment where the speed limit is 70 or 75. It wouldn't hurt anything, but I think that's about where the fuel mileage would start to drop off.)
Knucklehead97 Posted August 30, 2015 Author Posted August 30, 2015 Sorry, I meant 225/75r15. It's good to know that 3.55 gears will go good with them. I never drive over 65 unless I'm feeling sporty. I'm considering going to 235/75r15 since I'm having to buy a new set of tires anyways. Just can't decide haha!
Crash Posted August 30, 2015 Posted August 30, 2015 Just step up to the 235/75. And 3.55s will be good.
Knucklehead97 Posted August 30, 2015 Author Posted August 30, 2015 Will I experience any change of MPG or get up and go from the 235's as opposed to the 225's? It's only an inch bigger, I know.
Crash Posted August 30, 2015 Posted August 30, 2015 I've always had 235/75R15's or larger on the multiple XJ's I have owned. Combined with the 3.55 gears you will probably see an improvement. But, even with stock gears shouldn't affect much if at all. Really depends on the specific tires.
ScottJeep Posted August 30, 2015 Posted August 30, 2015 There is now a MJ Dana 35 3.55 sitting in my garage. It was removed for the MJ 4.11. To be different I just went with the MJ rear. The 4.11 was the trick for me, also knew I would go thru the 8.25 regarding brakes, bearings & seals... so all that plus all the welding I couldn't currently handle myself. My MJ is an automatic. With the 3.55 and 265/75/16 wheels/tires and my lift ( I am 2WD ) it averaged ~ 14mpg around town mixed driving.
Eagle Posted August 31, 2015 Posted August 31, 2015 Will I experience any change of MPG or get up and go from the 235's as opposed to the 225's? It's only an inch bigger, I know. Not even an inch. 6/10s of an inch -- 28.3" diameter vs. 28.9" diameter. But what really counts is revolutions per mile. From data I compiled many years ago, a 225/75-15 turns 730 revolutions per mile, and a 235/75-15 turns 722 revolutions per mile. That's a difference of 1.1 percent. In real world application, if a 225/75-15 with 3.55 gears turns 2100 RPM at 65 MPH in 5th gear, a 235/75-15 will turn 2077 RPM at 65 MPH. You'll never notice the difference.
Knucklehead97 Posted August 31, 2015 Author Posted August 31, 2015 Well. I shall probably go with 235's. I believe the shop said it would be 260 out the door for their cheapest street tire in that size... *sigh* there goes my Nates 4x4 rear bumper fund haha. Unless the shop has a GOOD used set of tires in either 225/75/15 or 235/75/15. If I could find a 3.55 geared MJ rear axle for cheap I would probably jump on it. Just for the simplicity of swapping.
Crash Posted August 31, 2015 Posted August 31, 2015 Check your local craigslist. I have found reasonable deals on there. Good tires are more important than a bumper. and honestly you are better off with something better than their bumper.
Knucklehead97 Posted August 31, 2015 Author Posted August 31, 2015 I haven't found any good tires on there lately sadly. The tires I just got were from a guy who deals in used goods and I thought he was giving me a good deal but in hindsite he screwed me over. My fault, though. I should have checked them out better. And I had the money put back for when they release a good coupon. Considering having a local weld shop build me one instead.
Lee21490 Posted August 31, 2015 Posted August 31, 2015 Check your local craigslist. I have found reasonable deals on there. Good tires are more important than a bumper. and honestly you are better off with something better than their bumper. Nates rear bumper is pretty damn good. I've bashed the hell out of it wheeling & havent really done any damage. Their cheap front bumper however, I've nearly destroyed already lol
Knucklehead97 Posted August 31, 2015 Author Posted August 31, 2015 I'm keeping my front bumper and just reinforcing it one day in the future. I love how the stock front bumper looks, especially with my grill guard. Nates just seems like it would be the best rear one for me as I just need something to pull a light trailer and that isn't a stock bumper. Not a big fan of the stock rear bumpers honestly.
Knucklehead97 Posted August 31, 2015 Author Posted August 31, 2015 Getting a set of Kenda street tires for $360 out the door tomorrow. 235/75r15 because they were actually cheaper. At least I won't have to worry about tires for a few years!!!
64 Cheyenne Posted September 1, 2015 Posted September 1, 2015 FYI there is a date code stamped on tires, generally a tire shop will not mount used tires on a passenger vehicle when the date code is over six years old.
Knucklehead97 Posted September 1, 2015 Author Posted September 1, 2015 I checked the code and they're 4 years old. I don't think the tire shop even checked the code or cared to check the sidewall for rot...
Eagle Posted September 1, 2015 Posted September 1, 2015 If they're dry rotted and cracked after just four years, they must be pretty crappy tires.
teamsmith Posted September 1, 2015 Posted September 1, 2015 Knucklehead, If you do go the 8.25 axle swap route, maybe I'll see if I can talk you into making the drive up to Chattanooga and helping me do the same.
Knucklehead97 Posted September 1, 2015 Author Posted September 1, 2015 I would love to! Gonna be a while before I do the swap though, probably. Got so much other stuff in line for the Jeep. And well, I'm at the tire shop right now... I misread the tire code. It was 11 years, not 4...
teamsmith Posted September 1, 2015 Posted September 1, 2015 11 years? That should be good news, huh? A tire shop shouldn't be selling 11 year old tires.
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